84 THE NERVOUS SYSTEM. 



nerve of the face, ear, palate, and tongue, (8) the au- 

 ditory or nerve of hearing, (9) the glosso-pharyngeal, 

 nerve of sensation and taste, (10) the pneumogastric 

 or vagus, which is both motor and sentory and governs 

 respiration, the heart, and the stomach, (11) the spinal 

 accessory, to the muscles of the soft palate, and (12) 

 the hypoglossal, the motor nerve to the tongue. 



The spinal nerves also are arranged in pairs: Eight 

 cervical pairs, twelve dorsal or thoracic, five lumbar, five 

 sacral, and one coccygeal, these titles denoting their 

 point of origin near the vertebra of the same name. 

 Each of these nerves arises by two roots, an anterior 

 motor root from the anterior horn of gray matter and a 

 posterior sensory root from the posterior horn, the latter 

 having a ganglion upon it. After emerging from the 

 cord the two roots unite to form the nerve, that the 

 nerve may contain both motor and sensory fibers. The 

 motor fibers are called efferent because they carry im- 

 pulses from the cord, while the sensory are called afferent 

 because they carry impulses back to the cord. After 

 leaving the cord the nerves unite to form plexuses, which 

 again divide into various nerve trunks and are distrib- 

 uted to the muscles. 



The first cervical nerves pass out of the spinal column 

 above the first cervical vertebra and the other cervical 

 nerves below that and the succeeding vertebrae, while 

 the other spinal nerves emerge each below the corre- 

 sponding vertebra, as the first dorsal below the first 

 dorsal vertebra, etc. After emerging they break up 

 into a large anterior division and a small posterior 

 division, the posterior branches supplying the spine and 

 the dorsal muscles and skin, the anterior the rest of the 

 trunk and the limbs. The cervical plexus is formed by 

 the anterior divisions of the first four cervical nerves, 

 the brachial plexus by the last four cervical and the first 

 dorsal or thoracic nerves, the lumbar plexus by the four 

 upper lumbar, and the sacral plexus by the last lumbar 

 and the four upper sacral nerves. 



